Added Smart Contract in Blockchain

[ShubhamTatvamasi]

Replace this sentence with a brief description of the awesome changes your PR has. 😊

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✅️ By submitting this PR, I have verified the following:

• Added descriptive name to PR
  • Your PR should NOT be called Update index.md, since it does not help the maintainer understand what has been changed.
  • For example, if you create a Variables article inside the Python directory, the pull request title should be Python: add Variables article.
  • Additional PR title examples:
    • Git: edit Git Commit article
    • PHP: create PHP section and add Data Structures article
• Reviewed necessary formatting guidelines in CONTRIBUTING.md.
• No plagiarized, duplicate, or repetitive content that has been directly copied from another source.

[QuincyLarson]

@ShubhamTatvamasi This is plagiarized directly from Wikipedia. Please don't waste our time.